In many control valve applications, and particularly in control valve applications involving severe service conditions, the internal components of the control valve may be subject to three phase flow with, for example, possible flashing, cavitation, and particles, all of which can potentially cause severe erosion and/or vibration. Consequently, such valves are often provided with carbide inserts that are corrosion resistant. The carbide inserts may be made of a ceramic material such as carbide, tungsten carbide, or other suitable materials.
In construction of such valve components, the carbide insert is typically attached to a housing using a shrink fit procedure where a metal retainer is heated, fitted, and then cooled to secure the carbide insert in place. It is possible that stress risers may be formed at the juncture between the carbide insert and the underlying base. Such stress risers can and sometimes do contribute to premature failure of the carbide insert by contributing to the formation and/or propagation of cracks in the carbide insert. Furthermore, temperature changes can cause the metal retainers to expand, thereby reducing the effectiveness of the metal retainer.
Other construction techniques include using mechanical stops, such as snap rings. However, mechanical stops may become unreliable during severe service conditions.
Referring now to FIG. 1, one known example of a flow control valve 10 includes a valve housing 12 having a fluid inlet 14 and a fluid outlet 16 connected by a fluid passageway 18. A trim assembly 20 is disposed within the valve housing 12 between the fluid inlet 14 and the fluid outlet 16. The trim assembly 20 includes a skirt 22 and a seat ring 24. A fluid control member, such as a plug 26 is disposed at least partially within the skirt 22 and the plug 26 interacts with the seat ring 24 to control fluid flow through the valve housing 12. The skirt 22 guides the plug 26 in reciprocating motion so that the plug 26 remains correctly aligned with the seat ring 24. A stem 28 is connected to the plug 26 at one end and to an actuator at another end. The actuator controls movement of the plug 26 within the skirt 22. A carbide insert assembly 29 includes a carbide insert 30, which is located within the valve housing 12, downstream of the seat ring 24. The carbide insert 30 may be attached to the valve housing 12 with a threaded connection 32. In other embodiments, the carbide insert 30 may be attached to the valve housing 12 by a shrink fit metal retainer (not shown) or by a mechanical stop (not shown), as discussed above.